The present invention relates to cantilevers for use in Scanning Probe Microscopies (abbreviated as SPM).
The types of scanning probe microscopy (SPM) include scanning tunneling microscopies (STM), atomic force microscopies (AFM), etc., which are used according to a physical quantity of object to be detected. Among these, AFM is suitable to detect a configuration of sample surface at high resolution and is used for measuring the surface configuration of semiconductor, optical disc, etc.
In AFM, for example, a cantilever having a probe portion at a terminal end thereof is provided and the probe portion is placed in a manner facing a surface of sample so that the cantilever is bent in accordance with the distance between the probe portion and the sample when an atomic force acts upon the probe portion from the sample surface.
The structure of conventional cantilever will now be described. FIG. 1 is a sectional view showing a known cantilever. Referring to FIG. 1, numeral 101 denotes a cantilever support portion made by processing a single-crystal silicon wafer and numeral 102 denotes a lever portion extended from the support portion 101. A probe portion 103 is formed toward a free end 104 of the lever portion 102. Here, the probe portion 103 is so disposed as to have its probe axis 105 perpendicular to the lever portion 102. It should be noted that, while a probe axis generally represents the axis connecting an apex of terminal end of the probe portion and a center of bottom surface of the probe portion 103 bordering the lever portion 102, it in the present invention represents a central axial straight line in the direction of length of a main body of base portion of the probe portion.
An exemplary construction of AFM apparatus as disclosed in Japanese patent laid-open application No. 2000-275260 is shown in FIG. 2 as an example of actual measuring by attaching a cantilever of such construction to AFM apparatus. It is shown here as that using the principle of optical leverage to optically detect a displaced condition of the cantilever. In particular, a displacement measuring laser beam 112 is radiated from a light source 120 onto the back surface of a cantilever 119. A reflection laser beam 113 reflected from the back surface of the cantilever 119 is received to optically detect at a light receiving device 121 the displacement of the cantilever 119 on the basis of changes in the position at which such light is received and the amount of the received light. The cantilever 119 is attached to AFM apparatus at a support portion 111 and set with an inclination of certain angle 117 with respect to the horizontal surface of a sample 116 to be measured which is placed on a cylindrical XYZ displacement actuator 118. Accordingly, the probe portion 115, formed on the terminal end of while having the probe axis perpendicular to the lever portion 114 extended from the cantilever support portion 111, faces the horizontal surface of the sample 116 to be measured with an inclination of the certain angle 117.
The above conventional cantilever has the problem as follows. First, as the terminal end portion of probe shown in an enlarged manner in FIG. 3, apex b of the terminal end portion of probe 115 does not necessarily come to the nearest position from the sample 116. Due to the fact that the lever portion is set with an inclination, there is a large possibility that distance B between the probe apex b and the surface of sample 116 becomes greater than distance A between point a at position shifted from the probe apex b and the surface of sample 116. As a result, the point of interaction between sample 116 and probe 115 is not determined to a certain one point. It is possibly at a position shifted from the center or the action is caused through a plurality of points. It thus becomes impossible to measure the irregularities on a sample surface accurately and at high resolution.
Further, when a convex part occurs on the sample surface in the case where the probe portion is scanned along the sample surface while it is continuously caused to oscillate at a constant amplitude in a direction perpendicular to the plane of the sample, a servo is to be actuated so as to keep the constant amplitude. However, if the probe portion is inclined in AFM measuring as described, a portion other than the apex of the terminal end of the probe portion is brought into contact with a side wall of the convex part before such an actuation of the servo. In addition to making the probe portion and sample vulnerable to damage, it becomes impossible for the terminal end portion of the probe portion to accurately take hold of the sample surface having a stepped portion for example in SPM measuring of a stepped sample surface having a steep sloping angle. An accurate SPM measuring cannot be performed.
Furthermore, in AFM measuring of the case where the angle of inclination of probe portion is to be corrected at SPM apparatus, a separate mechanism must be provided anew for example to tilt the sample stage in order to adjust the angle. A problem thus occurs that the number of parts of SPM apparatus is increased, resulting in an increased cost due to complication.
Moreover, with a cantilever having a conventional triangular pyramidal probe portion 121 as shown in FIG. 4A, measuring of the condition of a vertically raised side wall 123 of an irregular sample 122 is impossible up-to-date due to vertical angle of the probe portion 121. In other words, since the measurable side wall depends on the configuration of probe apex, only a side wall 123a of sloped surface as shown in FIG. 4B can be measured.
Further, it is difficult in forming to previously take the inclination of probe portion into consideration even in the case where the cantilever probe portion is formed from a single-crystal silicon or in the case where SiN film or the like is produced in a mold to form a probe portion by using a single-crystal silicon as the mold of the cantilever probe portion. Further, it is more difficult than the above to impart an inclination by bending the terminal end portion alone of the probe portion from the probe axis. It is difficult to be made even if the semiconductor processing technologies are applied.
While it is possible to sharpen the terminal end of cantilever probe portion by FIB (Focus Ion Beam) method, a vertical processing is a fundamental in such a case. It is very difficult to control the sharpened probe portion after the processing to a direction inclined from the probe axis by a certain angle. Further, since piece-by-piece work is performed in this technique, a reproducible probe portion is difficult to be formed.
Also in the case where CNT (Carbon Nano Tube), EBD (Electron Beam Deposition) probe is attached to the terminal end of cantilever probe portion, its attaching angle and direction to the terminal end of probe portion is difficult to be controlled. Further, since piece-by-piece work is performed also in this technique, forming of a reproducible probe portion is difficult in addition to inferior productivity.
Furthermore, since CNT is to be attached to a face at the terminal end of probe portion, it tends to be affected by roughness, angle, etc. of the face. It is thus necessary to previously form an inclined face in the original configuration of the cantilever probe portion in order that a certain angle of inclination between the probe axis and CNT is provided in the attaching. It is difficult to be controlled.